linux-kernel - Re: [lockdep warning] INFO: inconsistent lock state, serial8250_interrupt(), &port_lock

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Message-ID: <20080724071210.GA2738@gollum.tnic>
Date:	Thu, 24 Jul 2008 09:12:10 +0200
From:	Borislav Petkov <petkovbb@...glemail.com>
To:	Ingo Molnar <mingo@...e.hu>, Alan Cox <alan@...rguk.ukuu.org.uk>,
	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [lockdep warning] INFO: inconsistent lock state,
	serial8250_interrupt(), &port_lock_key

On Thu, Jul 24, 2008 at 08:53:29AM +0200, Borislav Petkov wrote:
> On Wed, Jul 23, 2008 at 11:36:04AM +0200, Ingo Molnar wrote:
> > 
> > * Ingo Molnar <mingo@...e.hu> wrote:
> > 
> > > =================================
> > > [ INFO: inconsistent lock state ]
> > > 2.6.26-tip-06509-gb4ebc67-dirty #13600
> > > ---------------------------------
> > 
> > the upstream component of that is: v2.6.26-6077-gc010b2f
> > 
> > i.e. my suspicion is that this got introduced via the recent tty 
> > changes.
> 
> Hi,
> 
> i hit the same warning here. How about the following fix (this is at least what
> i think happens):
> --
> 
> serial8250_startup() might unconditionally enable irqs after releasing
> &up->port.lock while we're still servicing an interrupt.

Actually, this explanation is not correct - it should be more like:

serial8250_startup() doesn't disable interrupts while taking the &up->port.lock
which might race against the interrupt handler serial8250_interrupt(), which
when entered, will deadlock waiting for the lock to be released.

> 
> Signed-off-by: Borislav Petkov <petkovbb@...il.com>
> 
> --
> diff --git a/drivers/serial/8250.c b/drivers/serial/8250.c
> index 27f34a9..55eca08 100644
> --- a/drivers/serial/8250.c
> +++ b/drivers/serial/8250.c
> @@ -1874,7 +1874,7 @@ static int serial8250_startup(struct uart_port *port)
>  		 * the interrupt is enabled.  Delays are necessary to
>  		 * allow register changes to become visible.
>  		 */
> -		spin_lock(&up->port.lock);
> +		spin_lock_irqsave(&up->port.lock, flags);
>  		if (up->port.flags & UPF_SHARE_IRQ)
>  			disable_irq_nosync(up->port.irq);
>  
> @@ -1890,7 +1890,7 @@ static int serial8250_startup(struct uart_port *port)
>  
>  		if (up->port.flags & UPF_SHARE_IRQ)
>  			enable_irq(up->port.irq);
> -		spin_unlock(&up->port.lock);
> +		spin_unlock_irqrestore(&up->port.lock, flags);
>  
>  		/*
>  		 * If the interrupt is not reasserted, setup a timer to
> 
> -- 
> Regards/Gruß,
>     Boris.

-- 
Regards/Gruß,
    Boris.
--
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